1. Field of the Invention
The present invention-relates to an integrated tuner circuit and to a television tuner using the integrated tuner circuit.
2. Description of the Related Art
The circuit configuration and the terminal arrangement of a conventional integrated tuner circuit (hereinafter referred to as an “integrated circuit”), and the connection relationships with peripheral circuits thereof are shown in FIG. 4. As shown in FIG. 4, a conventional integrated circuit 60 has 16 terminals for each of the two opposing sides (numerals within white circles represent terminal numbers (No.)).
Terminals No. 1 to No. 16 are provided for one of the sides 60a, and terminals No. 17 to No. 32 are provided for the other side 60b. Inside the integrated circuit 60, a plurality of circuits are formed, as generally shown in FIG. 4A balanced input end of a UHF mixer circuit 61 is connected to terminals Nos. 31 and 32, and an input end of a VHF mixer circuit 62 is connected to terminal No. 29. The balanced output ends of each of the mixer circuits 61 and 62 are connected to terminals Nos. 26 and 27.
Local oscillation signals are supplied to the VHF mixer circuit 62 from two oscillation circuits 63 and 64. A VHF low-band oscillation circuit 63 has two differential oscillation transistors 63a and 63b, the base of one of the oscillation transistors 63a is connected to terminal No. 1, and the collector of the other oscillation transistor 63b is connected to terminal No. 2. A VHF high-band oscillation circuit 64 also has two differential oscillation transistors 64a and 64b, the base of one of the oscillation transistors 64a is connected to terminal No. 4, and the collector of the other oscillation transistor 64b is connected to terminal No. 5.
A local oscillation signal is supplied from a UHF oscillation circuit 65 to the UHF mixer circuit 61. The UHF high-band oscillation circuit 65 also has two differential oscillation transistors 65a and 65b, the base of one of the oscillation transistors 65a is connected to terminal No. 6, and the collector thereof is connected to terminal No. 8. The base of the other oscillation transistor 65b is connected to terminal No. 9, and the collector thereof is connected to terminal No. 7.
Data for selecting a channel to be received is input from the main unit of a television receiver (not shown) to terminals Nos. 17 to 19. More specifically, a clock signal is input to terminal No. 17, channel selection data and band switching data are input to terminal No. 18, and address data is input to terminal No. 19. The above data is input to a PLL circuit 67 and a band-switching-voltage generation circuit 68 via an interface 66. A local oscillation signal is input to the PLL circuit 67 from each of the oscillation circuits 63, 64, and 65. An error signal output from the PLL circuit 67 is DC-converted by a charge pump 69 having a low-pass filter, and then a tuning voltage is output from a tuning-voltage generation circuit 70 to terminal No. 15. Furthermore, a reference signal is input to the PLL circuit 67 from a reference oscillation circuit 71. The oscillation connection end of the reference oscillation circuit 71 is connected to terminal No. 16.
The band-switching-voltage generation circuit 68 has therein a plurality of switching circuits, so that each switching circuit generates a high-level or low-level switching voltage in accordance with the input data. This switching voltage is used to switch the band to be received, and is output to each of terminals Nos. 20, 23 to 25, and 30.
A balanced type intermediate-frequency amplifying circuit 72 has two input ends connected to terminals Nos. 21 and 22, and two output ends connected to terminals Nos. 11 and 12.
Terminals Nos. 3, 10, and 28 are grounded, and a power-supply voltage B to be supplied to each circuit is applied to terminal No. 13.
Peripheral circuits connected to the integrated circuit 60 are externally provided. A television signal of a UHF band is input in a balanced manner to terminals Nos. 31 and 32 after passing through a UHF high-frequency amplifying circuit 73 and a UHF tuning circuit 74. A television signal of a VHF band is input to terminal No. 29 after passing through a VHF tuning circuit 75. The VHF tuning circuit 75 has therein a switching diode 75a, so that it tunes to a low band or a high band in accordance with the on/off state of the switching diode. The input ends of an intermediate-frequency tuning circuit 76 are connected to terminals Nos. 26 and 27, and the output ends thereof are connected to terminals Nos. 21 and 22.
A low-band resonance circuit 77 has a varactor diode 77a, one end thereof is coupled to terminals Nos. 1 and 2 via coupling capacitors 78 and 79, respectively, and the other end is grounded. A high-band resonance circuit 80 also has a varactor diode 80a, one end thereof is coupled to terminals Nos. 4 and 5 via coupling capacitors 81 and 82, respectively. Furthermore, a UHF resonance circuit 83 also has a varactor diode 83a, one end thereof is coupled to terminals Nos. 6 and 7 via coupling capacitors 84 and 85, respectively, and the other end is coupled to terminals Nos. 8 and 9 via corresponding coupling capacitors. An oscillation element 88, such as a crystal resonator, is connected to terminal No. 16.
In the above-described configuration, the tuning voltage output from terminal No. 15 is applied to the cathode of each of the varactor diodes 77a, 80a and 83a of the resonance circuits 77, 80 and 83, and the oscillation circuits 63 to 65 oscillate at a frequency necessary for their receiving band. The switching voltages output from terminals Nos. 23 and 24 are applied to the VHF tuning circuit 75, whereby the switching diode 75a is turned on or off. When the switching diode 75a is off, the VHF tuning circuit 75 tunes to the low band of the VHF band, and when the switching diode 75a is on, the VHF tuning circuit 75 tunes to the high band. Furthermore, the switching voltage output from terminal No. 30 is applied to the UHF high-frequency amplifying circuit 73. When a television signal of a UHF band is to be received, the switching voltage reaches a high level, causing the UHF high-frequency amplifying circuit 73 to operate at an appropriate bias state, and when a television signal of a VHF band is to be received, the switching voltage reaches a low level, causing the UHF high-frequency amplifying circuit 73 to stop operating.
In the manner described above, an intermediate-frequency signal is output from each of the mixer circuits 61 and 62 in such a manner as to correspond to each band to be received, and is output in a balanced manner to terminals Nos. 11 and 12 after passing through the intermediate-frequency tuning circuit 76 and the intermediate-frequency amplifying circuit 72. The output intermediate-frequency signal IF is processed by a demodulation circuit (not shown), etc.
Referring to FIG. 6, a description will now be given of the configuration of another conventional integrated tuner circuit and a television tuner using the integrated tuner circuit. FIG. 6 shows a television tuner to which, in particular, a television signal of a UHF band is input. An input tuning circuit 131 to which a television signal is input has a varactor diode (not shown), and a tuning voltage V is applied to the varactor diode. An FET (dual-gate FET) 132 which is a constituent of a high-frequency amplifying circuit is provided in a portion subsequent to the input tuning circuit 131, and the output end of the input tuning circuit 131 is coupled to a first gate of the FET 132.
One end of an inductance element 133 is connected to the first gate of the FET 132, and the other end is grounded at a high frequency by a DC-blocking capacitor 134 and is also grounded by a resistor 135. The source of the FET 132 is grounded, and a power-supply voltage B is applied to the drain thereof via a series circuit of a power-feeding resistor 136 and a choke inductor 137. The connection point of the power-feeding resistor 136 and the choke inductor 137 is grounded by a DC-blocking capacitor 138.
A double tuning circuit 139 is provided at the next stage of the FET 132. A parallel tuning circuit on the primary side thereof is formed of a varactor diode 139a and an inductance element 139b, and the connection point of the anode of the varactor diode 139a and the inductance element 139b, which is a high electrical-potential point, is coupled to the drain of the FET 132 via a coupling capacitor 140. The cathode of the varactor diode 139a is grounded by a DC-blocking capacitor 139c, and the other end of the inductance element 139b is also grounded. Then, a tuning voltage V is applied to the cathode of the varactor diode 139a. 
A parallel tuning circuit on the secondary side in the double tuning circuit 139 is formed of a varactor diode 139d and an inductance element 139e, and the connection point of the anode of the varactor diode 139d and the inductance element 139e, which is a high electrical-potential point, is coupled to a first terminal 142a of an integrated tuner circuit (hereinafter referred to simply as an “integrated circuit”) 142 via a coupling capacitor 141. The cathode of the varactor diode 139d is grounded by a DC-blocking capacitor 139f, and the other end of the inductance element 139e is also grounded. Then, a tuning voltage V is applied to the cathode of the varactor diode 139d. 
A mixer circuit 143 for converting the frequency is formed inside the integrated circuit 142. The mixer circuit 143 is formed as a balanced type, and their emitters are connected to each other. Also, the mixer circuit 143 has two transistors 143a and 143b whose bases are input ends, the base of one of the transistors 143a is connected to the first terminal 142a, and the base of the other transistor 143b is connected to the second terminal 142b. A bias voltage is applied to the bases of the two transistors 143a and 143b inside the integrated circuit 142. Furthermore, diodes 143e and 143d for preventing electrostatic breakdown, formed in the integrated circuit 142, are connected to the corresponding bases.
Furthermore, a band-switching-voltage generation circuit 144 is formed inside the integrated circuit 142. Data D of a channel to be received is input to the band-switching-voltage generation circuit 144, and a high (approximately equal to the power-supply voltage B) and a low (approximately 0 volts or an open state) switching voltage for selecting a band belonging to that channel in accordance with the data D is generated. The switching voltage reaches a high level, for example, when a television signal of a channel in the UHF band, which is a high frequency band, is received, and reaches a low level when a television signal of a channel in the VHF band, which is a low frequency band, is received. The output end of the band-switching-voltage generation circuit 144 is connected to a third terminal 143c. 
The first terminal 142a and the second terminal 142b are connected to each other through an inductance element 145. Furthermore, the third terminal 143c is connected to the connection point of the inductance element 133 and the resistor 135 through a resistor 146.
Furthermore, the tuning voltage V to be applied to the input tuning circuit 131 and the double tuning circuit 139 is preferably generated from the integrated circuit 142.
In the above-described configuration, when a television signal of a UHF band is to be received, the switching voltage becomes high, an appropriate bias voltage is applied to the first gate of the FET 132, and the FET 132 operates normally. The television signal which is amplified by the FET 132 and is then selected by the double tuning circuit 139 is converted in a balanced manner by the inductance element 145, and is input to the first terminal 142a and the second terminal 142b of the integrated circuit 142.
When a television signal of the VHF band is to be received, the switching voltage becomes low, a bias voltage is not applied to the first gate of the FET 132, and the FET 132 is placed in a non-operating state.
In the above-described conventional integrated circuit, many terminals are used so that a resonance circuit is coupled to an oscillation circuit. The number of terminals for extracting a switching voltage from the band-switching-voltage generation circuit is great, and the number of terminals to be grounded is great. For this reason, the connection with peripheral circuits is complex, and the size of the integrated circuit itself cannot be reduced. Furthermore, the size of the television tuner which uses the integrated circuit cannot be reduced.
In the above-described configuration shown in FIG. 6, a switching voltage is used to switch the FET 132 between the operating state and the non-operating state. For this purpose, a dedicated third terminal 142c is provided in the integrated circuit 142. In order to reduce the size of the integrated circuit 142, a reduction in the number of terminals is an important task.